Beverage cans are produced in massive quantities in high speed equipment. One aspect of modern beverage can manufacturing is can decoration in a specialized machine referred to as a decorator. An example of a prior art decorator is shown in U.S. Pat. No. 5,337,659. Commercial can decorators are sold, for example, by Stolle Machinery and Formatec.
As described in the 659 patent, many commercial can decorators include an infeed conveyor that receives cans from a can supply and directs them to accurate cradles or pockets along the periphery of a pocket wheel. The pocket wheel is fixed to a continuously rotating mandrel carrier wheel or spindle disc, which in turn is fixed to a continuously rotating horizontal drive shaft. Horizontal spindles or mandrels, each being pivotable about its own axis, are mounted to the mandrel carrier wheel adjacent its periphery.
While mounted on the mandrels, the cans are decorated by being brought into engagement with a blanket (e.g., without limitation, a replaceable adhesive-backed piece of rubber) that is adhered to a blanket segment of the multicolor printing unit. The blankets are carried by a blanket drum. Then the outside of each decorated can is coated with a protective film of varnish applied by an overvarnish unit. The decorated and coated cans are transferred from the mandrels to a transfer wheel and then to generally horizontal pins carried by a chain-type output conveyor, which carries the cans through a curing oven.
Conventional decorators are driven by a single motor and a series of shafts, tensioners, chains/belts and gearboxes to each of the four main shafts (that is, the shafts for the blanket drum, spindle disc, transfer wheel, and pin chain drive). In other words, the drives are mechanically linked and once the relative timing positions to each other are set, they rarely move. The overvarnish unit shaft is driven by a separate motor (that is, prior art overvarnish units are not mechanically linked to the drive system that mechanically drives the blanket drum, spindle disc, transfer wheel, and pin chain drive) to provide different speeds to allow different numbers of ‘wraps’ or coatings of varnish depending on customer specification.
Regarding applying images to the cans, while moving toward engagement with an undecorated can, the blanket engages a plurality of printing cylinders, each of which is associated with an individual ink station assembly or inker. Each inker produces a controlled film of ink that is applied to the printing cylinder. Typically, each inker provides a different color ink and each printing cylinder applies a different image segment to the blanket. All of these image segments combine to produce the same main image that is transferred to the can body. Accordingly, registration of the print cylinders is crucial to image quality.
A common way for operators to register the print cylinders is to inspect the can image at the blow off position, then manually adjust the radial and axial registration close to the plate cylinder on the machine underneath the inking units. This is normally by a platform that is in front of the colour section.
For each plate cylinder there are two mechanical assemblies that either push/pull the plate cylinder for the axial registration or rotate the plate cylinder for radial registration. The operator uses various tools to loosen the assembly allowing it to move and then reverses the process for tightening it. This process of adjusting the axial and radial position of the plate cylinder can be repeated several times in each inker position to register the image. Typically a can may have anything from 4 to 8 colours and therefore the registration process is repeated for the number of colours being used.
Typically there are two operators that perform the registration operation. One operator is on the platform and one close to the blow off point where the printed cans are inspected. The operator at the blow off point collects two cans, inspects one and throws the other to his colleague on the platform. After a discussion and assessment of the image, they agree on what needs to move and by how much. The operator then makes the manual adjustments until both are happy with the registration in all positions. The process of determining the quality of the image and determining the direction and magnitude of the axial and radial adjustments of the plate cylinders requires skill and experience.